Equalization circuit

Abstract

A frequency equalization circuit includes an active filter circuit. The filter circuit differentiates the input signal. A plurality of adjustable resistances are connected to the differentiator corresponding to a plurality of operating or frequency ranges. A switch selects one resistance in accordance with one selected operating range to connect the filter circuit to an amplifier.

What is claimed is: 
     
       1. An equalization circuit comprising: an input .Iadd.terminal.Iaddend.;   amplifying means .Iadd.having an input .Iaddend.connected to said input .Iadd.terminal.Iaddend.;   filter circuit means having an output .[.connected.]. .Iadd.for connection .Iaddend.to said input .Iadd.of said amplifying means and .Iaddend.for providing a signal varying in amplitude with frequency at its output;   a plurality of adjustable resistances corresponding to a plurality of operating ranges connected to the output of said filter circuit means for adjusting the signal amplitude provided by the output; and   switch means for selectively connecting one of said plurality of adjustable resistances to said .Iadd.input of said .Iaddend.amplifying means according to one selected operating range.   
     
     
       2. The circuit of claim 1 wherein: said filter circuit means provides a signal which rises with frequency.   
     
     
       3. The circuit of claim 1 wherein: said filter circuit means comprises an RC series circuit .[.connect.]. .Iadd.connected .Iaddend.to said input .Iadd.terminal.Iaddend..   
     
     
       4. The circuit of claim 1 wherein: said filter circuit means comprises active filter means.   
     
     
       5. The circuit of claim 1 wherein: said filter circuit means comprises differentiating means.   
     
     
       6. An equalization circuit comprising: an input terminal;   a first amplifier having an input and an output;   an input resistance connected between said input terminal and the input of said first amplifier; and,   a filter circuit connected in parallel with said input resistance including: circuit means having an output to filter a signal received at said input terminal;   a plurality of adjustable resistances connected to the output of said filter circuit means, each of said resistances selected according to a different one of a plurality of operating ranges for adjusting the amplitude of the signal provided by said filter circuit means; and,   switch means connected between said plurality of adjustable resistances and the input of said first amplifier for selectively connecting said adjustable resistances to said first amplifier.     
     
     
       7. A circuit of claim 6 wherein: said filter circuit means provides a signal varying with frequency.   
     
     
       8. The circuit of claim 6 wherein: said filter circuit means provides a signal rising with frequency.   
     
     
       9. The circuit of claim 8 wherein: said filter circuit means includes an RC circuit connected to said input terminal and a second amplifier connected to said RC circuit, the output of said second amplifier being connected to said plurality of adjustable resistances.   
     
     
       10. The circuit of claim 9 wherein: said switch means comprises a plurality of contacts connected respectively to said plurality of variable resistances; and further including:   a plurality of frequency pre-emphasis means connected respectively between said plurality of contacts and the output of said first amplifier.   
     
     
       11. The circuit of claim 6 wherein: said filter circuit means comprises an RC series circuit connected to said input terminal.   
     
     
       12. The circuit of claim 6 wherein: said filter circuit means comprises active filter means.   
     
     
       13. The circuit of claim 6 wherein: said filter circuit means comprises differentiating means. .Iadd. 14. An equalization circuit, comprising:   a. an input terminal for receiving an input signal to be equalized;   b. a first amplifying means having an input and an output;   c. a first means for connecting said first amplifying means to said input terminal and providing an output signal which is substantially in phase with said input signal;   d. a phase shift circuit means coupled to said input terminal and providing an output signal having an increasing amplitude and constant phase lag with frequency relative to said input signal, within a predetermined frequency range of said input signal;   e. a second means for connecting the output of said phase shift circuit means to said input of said first amplifying means; and   f. said first amplifying means providing an output signal representative of the sum of said respective output signals provided by said first   
     
     
        connecting means and said phase shift means. .Iaddend..Iadd. 15.  The circuit of claim 14 wherein: said phase shift circuit means provides an output signal increasing in amplitude and lagging in phase by 90°. .Iaddend..Iadd. 16. The circuit of claim 15 wherein:   said phase shift circuit means comprises an inverting differentiating operational amplifier means. .Iaddend. .Iadd.17. The circuit of claim 14 wherein said second connecting means comprises a plurality of variable resistances and switch means for selectively connecting one of said plurality of variable resistances to the input of said first amplifying means. .Iaddend. .Iadd. 18. The circuit of claim 14 wherein said second connecting means comprises a resistive means. .Iaddend. .Iadd. 19. An equalization circuit comprising:   a. an input terminal for receiving an input signal to be equalized;   b. a first amplifying means having an input and an output, said input of the first amplifying means coupled to said input terminal to receive a signal which is substantially in phase with said input signal;   c. a second amplifying means having an input, an output, a feedback resistor connected between said output and input to provide negative feedback, and a capacitive reactive impedance means coupled between said input terminal and the input of said second amplifying means, said second amplifying means providing an output signal increasing in amplitude and having a constant phase lag with frequency relative to input signal within a predetermined frequency range of said input signal; and   d. means for connecting the output of said second amplifying means to said input of said first amplifying means. .Iaddend. .Iadd. 20. The circuit of claim 19 wherein:   said connecting means comprises a plurality of variable resistances; and   switch means for selectively connecting one of said plurality of variable resistances to the input of said first amplifying means. .Iaddend..Iadd. 21. The circuit of claim 20 wherein:   said switch means further comprises a plurality of contacts connected respectively to said plurality of variable resistances; and further including a plurality of frequency pre-emphasis means connected respectively between said plurality of contacts and the output of said first amplifying means. .Iaddend.